An airplane is propelled by one or several propulsive assemblies each comprising a turboshaft engine housed in a substantially tubular nacelle. Each propulsive assembly is attached to an aircraft by a mast situated under a wing or at the fuselage.
A nacelle generally has a structure comprising an air intake upstream of the engine and a middle section able to surround a fan of the turboshaft engine, a downstream section generally housing thrust reverser means and able to surround the combustion chamber of the turboshaft engine. The nacelle typically ends with an ejection nozzle, the outlet of which is situated downstream of the turboshaft engine.
The air intake comprises, on one hand, an intake lip adapted to allow optimal collection towards the turboshaft engine of the air necessary to supply the fan and the internal compressors of the turboshaft engine, and on the other hand, a downstream structure, on which the lip is attached, intended to suitably channel the air towards the blades of the fan. The assembly is attached upstream of a case of the fan belonging to the upstream section of the nacelle.
In flight, depending on the temperature and moisture conditions, ice can form on the nacelle in various places including the outer surface of the air intake lip. The presence of ice or frost modifies the aerodynamic properties of the air intake and disturbs the conveyance of the air towards the fan.
Moreover, aircraft turboshaft engines generate significant noise pollution. There is a high demand aiming to reduce this pollution, even more so given that the turboshaft engines used are becoming more and more powerful.
In order to further improve the acoustic performance of aircrafts, in particular turboshaft engine aircrafts, nacelles are provided with acoustic panels aiming to attenuate the noise generated by the turboshaft engine as well as the vibrations of the structures.
Acoustic panels are structures well known for absorbing noise. These panels usually include one or several layers of cellular core structures (commonly referred to as a “honeycomb” structures). These layers are coated on the lower face, i.e. not in contact with the flow of air inside the nacelle, with a so-called “non perforated or solid” skin impermeable to air, and on their upper face, i.e. in contact with the flow of air inside the nacelle, with a so-called “acoustic” perforated outer skin permeable to air.
One solution for de-icing or preventing the build-up of ice on the outer surface of the air intake lip consists of heating the walls of the air intake lip using an electric resistance.
The electric resistance is generally mounted on or in the outer wall of the air intake lip on the side with the cold air penetrating the nacelle.
In order to increase the treated acoustic surface of the air intake lip, it is possible to acoustically treat part of the lip. However, it is necessary to make the acoustic treatment compatible with the de-icing method using an electric resistance, which is difficult to achieve.